What to Know About the Operation to Retake Mosul

The battle to liberate the Iraqi city of Mosul from ISIS militants began on Monday, in the biggest military operation since the departure of the U.S. from the country in 2011.

In a broadcast on state television early Monday morning, Iraqi Prime Minister Haider al-Abadi announced the start of the operation. “These forces that are liberating you today, they have one goal in Mosul which is to get rid of Daesh and to secure your dignity. They are there for your sake,” he said in an address to the city’s residents, using the Arabic acronym for ISIS. “God willing, we shall win.”

The operation to drive ISIS out of the city is of key strategic importance to the Iraqi government and its military, which surrendered and abandoned Mosul to the control of ISIS forces in June 2014. The U.S. is backing the coalition effort with air strikes and tactical support, with Secretary of Defense Ash Carter calling the operation a “decisive moment in the campaign” to defeat ISIS.

Here’s what to know about the city of Mosul and the operation to liberate it:

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Where is Mosul and why is it an important city? Mosul is a city in northwestern Iraq that was previously home to around 2 million people before it was captured by ISIS. Once rich in historical buildings and ancient sites, the city is the capital of Nineveh province and is home to the historic Mosul museum. It was a city with a military reputation, which is what made its surrender a shock to Iraqi officials.

Mosul has strategic significance – it is located near the borders with Turkey and Syria, where ISIS rebels have joined the insurgency against the Syrian regime led by President Bashar Assad. The city is also home to the Mosul dam, which was built by Saddam Hussein – an important structure that was reclaimed from ISIS control in 2015.

The city’s political situation is complicated by the fact that it is surrounded by the Kurdish-controlled region of Iraq, which does not answer to the central government in Baghdad. This, combined with sectarian tensions between Sunni and Shiite fighters, and the involvement of the U.S., has hindered cooperation in previous coalition efforts to liberate the city.

How long has it been held by ISIS? Over two years. It is now the group’s last remaining urban stronghold in the region, and has been central to the group’s ideology and ambitions since leader Abu Bakr al-Baghdadi declared the establishment of a caliphate from the city in June 2014 after its capture. ISIS’s continuing control over the city and its resources act as symbols of prestige and a way for the group to validate its claim that it is building a caliphate.

How many civilians live in the city? It is estimated that between 600,000 and 1 million people live in Mosul now, a decrease since ISIS took control two years ago. Civilians have lived under strict Islamic laws since then, with recent reports of brutal crackdowns on those trying to escape the city. In the lead up to the operation, the Iraqi government urged civilians to stay in their homes through radio broadcasts and dropping leaflets over the city in an effort to prevent citizens from panic evacuation which could lead to deaths in crossfire. Still, the United Nations has warned of a possible humanitarian catastrophe in the battle over the city.

What forces are part of the coalition that is fighting in the operation? More than 25,000 troops, including paramilitary forces made up of Sunni tribal fighters and Shiite militias, will take part in the offensive that will be launched from five directions around the city. They will be trying to liberate the city from the estimated 4,000-8,000 ISIS fighters defending Mosul.

According to the BBC, the main assault on the city is being led by Iraqi army troops based south of Mosul, with around 4,000 Kurdish Peshmerga militia charged with clearing villages in the east. Local Sunni tribal fighters will be fighting alongside Shia-led paramilitary forces, despite the ancient and hostile rivalry between the two denominations of Islam. Additional support from the U.S.-led coalition against ISIS is being provided in the form of air support, artillery fire and advisory personnel on the ground.

How long is the operation expected to take? The multi-phase operation to recapture the city is expected to last weeks, if not months. Operation commander Major General Najm al-Jabouri told Reuters that victory by the end of the year would be likely due to the death of top ISIS leaders in targeted air strikes over recent months, echoing the promises of Prime Minister Haider al-Abadi.

“Urban warfighting is not easy and this is a large city that has had at least two years to prepare to defend its position … It’s going to be a multi-dimensional fight,” said Lieutenant General Vincent Stewart, Director of the U.S. Defense Intelligence Agency, at a national security summit in Washington last month, Reuters reported.

Which other cities has the Iraqi army liberated? Iraqi forces have defeated ISIS in other key cities of Tikrit, Ramadi and Fallujah. The reclaiming of Fallujah, a city 40 miles west of Baghdad, earlier this summer was an important step in the preparations for the Mosul operations. The management of the movement of civilians in the Fallujah operation was seen as chaotic and inadequate, although the city was liberated more quickly than expected after five weeks of fighting and encouraging signs of cooperation amongst the pro-government coalition.

What happens next? After Turkey’s President Recep Tayyip Erdogan said on Monday that Turkey will be committing troops to the offensive in Mosul, managing the various forces fighting alongside the Iraqi government will be a delicate challenge. The battle’s humanitarian fallout will also be a significant test. In a statement, Stephen O’Brien, the U.N.’s under-secretary for humanitarian affairs and emergency relief coordinator, urged all those involved in the conflict to “protect civilians and ensure they have access to the assistance they are entitled to and deserve.”